The defaults on the DAQ Assistant are 100 samples aquired at 1 kHz, so every cycle you are getting 100 data points. If you only want 2 points a second and software timing is acceptable, you could just wire "1" to the number of samples on the DAQ Assistant (or right-click and select Properties to configure the node) and use a timed loop or a software delay in the loop like "Wait until next ms multple". Alternatively, you could use more advanced vis such as "DAQmx Read" to get the behavior you want. Remember that the DAQ operation will return as soon as it gets the data you instructed it to capture, so you'll probably need something to keep things periodic between loop cycles unless you want to move to continuous hw timed DAQ operation.
